Hey, I think, the funny part is that Charlie thinks his brother is not that smart, and he tells him things that everybody knows. It's something like, 'Wash your hands after you have been to the toilet!'. (Said when a close friend, not a child, wants to use your WC.) Everybody should know how to use a telephone.

In the US, you have to dial a "1" before making a long distance phone call from a landline. Growing up, my grandmother had the same area code as me, but it was a long distance call, so I had to dial 1 + area code + phone number, whereas a local call with the same area code only required dialing the phone number itself. You'd get a message from the phone company saying "You must first dial a 1 or 0 before calling this number" if you messed up! I think it is just how landline telephone providers distinguish between local vs long-distance calls for billing purposes, although the country code for the US is also +1. I've never watched the show to know why this would be funny in context, though!

"You have to dial 1 first" means you need to add the area code (1) before dialling the number "oxofempal".